![]() When the health of this vegetation is compromised, associated wildlife suffers. ![]() These river-based engineering processes establish habitat for hundreds of resident and migratory birds and for wetland-partial fishes like the endangered Gila topminnow. In flood season, rushing water can remove patches of undergrowth, creating structurally diverse mosaics of open areas and dense vegetation. In the arid Sonoran Desert, such flooding events are essential for survival and recruitment of riverine trees, understory vegetation, marshes and cienegas. High-level flows breach the riverbank, soaking water into the ground outside the immediate vicinity of the shore, and thereby replenishing groundwater. These varied flow patterns also maintain the structural integrity of the native cottonwood-willow forests that line the Gila system’s rivers and streams, essential breeding habitat for the endangered southwestern willow flycatcher and threatened western yellow-billed cuckoo. Every step of native fish reproduction happens in delicate coordination with the snowmelt-fed spring flow, but by the end of the century, the American West may be functionally devoid of snowpack due to climate change. Once larvae hatch, the spring flow has already started to lessen, so the larvae avoid the brunt of the strongest currents. Specific cues of temperature and flow intensity trigger these species to spawn. In early spring, sedimentation increases, but by late spring, rapidly receding flows carry away fine sediment to reveal cobble bars-a micro-ecosystem with nooks and crevices sheltering invertebrate prey and smooth surfaces perfect for egg-laying, providing fish like the endangered spikedace reproductive habitat. Spring flows annually reshape river bottoms. While these feats of engineering made possible a bustling metropolis in the midst of an inhospitable desert, they did so by imperiling the biological world of the Gila River and its tributaries. CAP transports billions of gallons of water from the Colorado River to central and southern Arizona each year to support agriculture and the water needs of cities like Phoenix and Tucson. But even this water proved insufficient, so Arizona lawmakers began construction of the Central Arizona Project (CAP), a 336-mile-long aqueduct completed in 1993 at a cost of $4 billion. Major changes in 1911, when the federal government completed the Roosevelt Dam on the Salt River and the Coolidge Dam on the Gila itself in 1928, resulted in a massive increase in the valley’s population, and as agricultural demand outpaced what could be taken from the river, farmers started pumping groundwater on a large scale. How did the Gila River system become so degraded? Agriculture and human settlement are not new to the region-the ancient Hohokam civilization flourished by building hundreds of miles of complex irrigation canals drawing water from the Gila. But it was not until the late 19th century that white settlers in the Gila River Valley began restructuring the river by building small-scale dams and diversions to protect their crops from floods and droughts. As a result, 21 of Arizona’s original 36 native fish species are either extinct or federally listed as threatened or endangered. West of Phoenix, the river is usually a dry bed and where water still flows, the fragile ecosystem is assaulted by invasive species, drought, grazing and mining, which are only exacerbated by the growing effects of climate change. However, what was once the lifeblood of the Sonoran Desert has been drained and diverted to support the ever-growing metropolises of Phoenix and Tucson.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |